Optical objective



Search Roon SR 0R 2,419,844

A. WARMISHAM ETAL OPTICAL OBJECTIVE Filed July 2. 1945 R F/G,

3 R4 Rs @#2629 +4795 aa/22 .53485 R7 -3-oes April'zs, 1947.

DI 05 .OS/ D4 F/Ga.

In ventola By c- MMA W naw A ltorneys Patented Apr. 29, 1947 UNITED STATES Search Roca PATENT GFFICE OPTICAL OBJECTIVE Application July 2, 1943, Serial No. 493,275 In Great Britain August 26, 1942 24 Claims.

This invention relates to optical objectives for photographic or like purposes, comprising two or more divergent elements and two or more convergent elements, and corrected for spherical and chromatic aberrations, coma, astigmatism, curvature of field and distortion, and having small zonal spherical aberration.

It is well-known to provide paraxial chromatic correction in a doublet in respect of two colours, for example red and green, by the use of an appropriate combination of crown and flint glass, but owing to the different relative partial dispersions of the two kinds of glass the correction does not extend throughout the spectrum, and there is a residual colour aberration known as secondary spectrum. Reasonably good correction can be obtained in the well-known triplet objective, which however does not provide correction for field curvature or astigmatism.

The present invention has for its object to provide good correction for secondary spectrum in a photographic or like objective having small zonal spherical aberration without sacrificing correction for astigmatism, iield curvature and distortion.

The necessary conditions can be expressed mathematically as follows. If fp and 'mp are respectively the focal length and the magnification of a lens element p having refractive indices nc, nn, ne, np, ng, respectively for the lines CDeFg Abb V number and relative partial dispersion then good secondary spectrum correction is obtained if and for all the elements of the objective. It should should be made clear that the magnication mp, herein referred to, may be dened as being equal to the ratio hp/hi, where hp and h1 are respectively the ordinates of the points of intersection with the lens element p and with the first lens element of a paraxial ray of the wave-length of the D-line through the conjugate points for which the objective is corrected.

(cl. sii-57) In the objective according to the present invention one of the divergent elements is made of a crystalline alum and is cemented between two convergent elements of optical glass.

The crystalline alum may be of the double sulphate class, and preferably incorporates alumim'um sulphate combined with an alkaline sulphate as represented by the general formula RnSO4 A12(SO4)a.24HzO, wherein R represents a monovalent metal or a monovalent radicle, for example potassium or sodium or ammonium.

The two convergent elements cemented to the alum crystal element are preferably made of glasses whose mean refractive indices differ from that of the crystal by more than .1 and less than .25, whilst the Abb V numbers of the glasses used for all the convergent elements lie between 45 and 62. Dense fiint glass is preferably used for one of the divergent elements.

'I'he objective may be arranged in various ways, but conveniently has either its front component or its rear component convergent and of cemented triplet construction including the crystalline alum element as its middle element. 'I'hus the objective may consist of4 a simple divergent component located between two convergent components, of which one is simple and the other is of cemented triplet construction. In such objective dense iiint glass is preferably used for the simple divergent middle component.

In the accompanying drawings Figure 1 illustrates -an objective according to the invention having three components of which the front component is a convergent triplet including a potash alum element and the second and third components are simple and are respectively divergent and convergent,

Figure 2 shows an objective differing from that of Figure 1 in that the rear component is the triplet containing the potash alum element, the

front component being simple, and

Figures 3 and 4 respectively show objectives similar to that of Figure 1 but using sodium alum and ammonium alum instead of potash alum.

Numerical data for these four examples are given in the following tables, in which R1, Rz represent the radii of curvature of the individual lens surfaces counting from the front (that is the side of the longer conjugate), the positivev sign indicating that the surface is convex to the 3 fractive indices no for the D-line, the Abb V numbers and the relative partial dispersions for the intervals (e to g) (C to F) of the glasses or crystals used for the individual elements.

Example I Equivalent focal length 1.000 Relative Aperture F/2.7

Thickness or Relative Refractive Abb V Radius Air Separa- Partial tion Index u number Dispersion D1 .0556 1. 613 59. 3 .999 Rz-3.086

D: .0648 l. 613 59. 3 .999 R4-H. 795

S1 .0741 Rs. B122 .Di .0231 l. 652 33. 5 l. 000 R+. 3485 Ds .0556 l. 613 59. 3 .999 Rs. 5324 Example II Equivalent focal length 1.000 Relative Aperture F/2.7

Thickness or Relative Refractive Abb V Radius Air Se ara- Partial ting Index n number Dispersion I): .0812 1.644 48. 3 1.025 Bri-l0. 148

Si 0761 Ra-.6752

D: 0254 1. 697 30. 5 l. 067 R4+. 4528 Se 0629 Rsi-2. 169

D: .0964 1. 013 59. 3 .999 Rs. 2689 .D4 .0152 l. 456 58.1 .928 R7+. 0766 D5 0507 l. 644 48. 3 l. 025 Rs-.8407

These two examples both use potash alum crystal for the divergent middle element of the triplet component cemented between two convergent elements of optical glass. and they differ from one another primarily in that in Example I it is the convergent front component and in Example II it is the convergent rear component.

which is of triplet construction. Both examples employ dense int glass for the simple divergent middle component, and in Example I the three convergent elements are all made of the same crown glass, whilst in Example II crown glass is used for one of the convergent elements and dense barium int glass for the other two.

Example III Equivalent focal length 1.000 Relative Aperture F,l2.9

Thickness or Relative Refractive Abb V Radius Air Separa Partial tion Index n.. number Dispersion D1 .0556 1.613 59.3 .999 Rz3. 091

Dz .0185 1.4388 57.8 .909 Rrr-.2633

Dz .0649 1.613 57.6 1.005 Rui-1.798

Si .0742 Ris-.8134

Ds .0556 1.613 55.7 1.010 Rt-. 5224 These two examples are both generally similar to Example I but use in Example III sodium alum and in Example IV ammonium alum in place of the potash alum. They each use dense flint glass for the simple divergent middle component and crown glass for the three convergent elements.

It; will be appreciated that the above arrangements have been described by way of example only and that; the invention may be carried into practice in other ways.

What we claim as our invention and desire to secure by Letters Patent is:

1. An optical objective, corrected for spherical and chromatic aberrations, coma, astigatism, field curvature and distortion, and comprising three components in axial alignment of which the front and rear components are convergent and the middle component divergent. one of the convergent components being of cemented triplet construction having a focal length between .5 and .7 times the focal length of the complete objective, such triplet component consisting of a double-concave divergent middle element made of crystalline alum of the double Sulphate class having the formula R2SO4.A12(SO4)3 with water of crystallization. wherein R represents a monovalent metal or monovalent radical, and two convergent element-s of optical glass between which said middle element is cemented, the algebraic sum of the curvatures of the two cemented surfaces lying between 2 and 4 times the reciprocal of the focal length of the whole triplet component, one cemented surface having a radius of curvature more than twice that of the other cemented surface.

2. An optical objective corrected for spherical and chromatic aberrations, coma, astigatism, field curvature and distortion, and comprising three components in axial alignment of which the front and rear components are convergent and the middle component divergent, one of the convergent components being of cemented triplet construction having a focal length between .5 and .7 times the focal length of the complete objective, such triplet component consisting of a double-concave divergent element made of crystalline alum of the double sulphate class having the formula R2SO4.A12(SO4)3 with water of crystallization. wherein R represents a monovalent metal or monovalent radical, cemented between two convergeht elements made of glasses whose mean refractive indices differ from that of the crystal element by more than .1 and less than .25 and whose Abb V numbers lie between 45 and 62, the algebraic sum of the curvatures of the two cemented surfaces lying between 2 and 4 times 568ml] KOU the reciprocal of the focal length of the whole triplet component, one cemented surface having a radius of curvature more than twice that of the other cemented surface.

3. A triplet lens component, comprising a double-concave divergent middle element made of crystalline alum of the double sulphate class having the formula R2SO4.A12(SO4)3 with water of crystallzation, wherein R represents a monovalent metal or monovalent radical, and two convergent elements of optical glass between which said middle element is cemented, the algebraic sum of the curva-tures of the two cemented surfaces lying between 2 ancl 4 times the reciprocal of the focal length of the whole triplet component, one cemented surface having a radius of curvature more than twice that of the other cemented surface.

4. A triplet lens component comprising a double concave middle element made of crystalline alum of the double sulphate class having the formula R2SO4.A12(SO4)3 with water of crystallization, wherein R represents a monovalent metal or monovalent radical, and two convergent elements between which the middle element is cemented, such convergent elements being made of glasses whose mean refractive indices differ from that of the crystal by more than .l and less than .25 and Whose Abb V numbers lie between 45 and 62, the algebraic sum of the curvatures of the two cemented surfaces lying between 2 and 4 times the reciprocal of the focal length of the whole triplet component one cemented surface having a radius of curvature more than twice that of the other cemented surface.

5. An optical objective, corrected for spherical and chromatic abberations, coma, astigmatism, field curvature and distortion, and comprising three components in axial alignment, of which the front and rear components are convergent and the middle component divergent, the divergent component and one of the convergent components being simple and made of optical glass, whilst the other convergent component is in the form of a cemented triplet having a focal length between .5 and .7 times that of the complete objective, such triplet component consisting of a double-concave divergent middle element made of crystalline alum of the double sulphate class having the formula R2SO4.A12(SO4)3 with water of crystallization, wherein R represents a monovalent metal or monovalent radical, and two convergent elements of optical glass between which said middle element is cemented, the algebraic sum of the curvatures of the two cemented surfaces lying between 2 and 4 times the reciprocal of the focal length of the whole triplet component, one cemented surface having a radius of curvature more than twice that of the other cemented surface.

6. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortions; and comprising a meniscus-shaped convergent front component of cemented triplet construction having its outer surfaces convex to the front and having a focal length between .5 and .'7 times that of the complete objective, a convergent simple rear component made of glass having an Abb V number between 45 and 62, and a divergent simple middle component made of dense int glass, the triplet front component consisting of a double-concave divergent element made of crystalline alum of the double sulphate class having the formula RzSO4.A12(SO4)s with water of crystallization,

wherein R represents a monovalent metal or monovalent radical, cemented between two convergent elements made of glasses whose Abb V numbers lie between 45 and 62 the algebraic sum of the curvatures of the two cemented surfaces lying between 2 and 4 times the reciprocal of the focal length of the whole triplet component, one cemented surface having a radius of curvature more than twice that of the other cemented surface.

7. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, eld curvature and distortion, and comprising a double-convex convergent rear component of cemented triplet construction having a focal length between .5 and .7 times that of the complete objective, a convergent simple front component made of glass having an Abb V number between 45 and 62, and a divergent simple middle component made of dense flint glass, the triplet rear component consisting of a double-concave divergent element made of crystalline alum of the double sulphate class having the formula R2SO4.A12 SO4)3 with water of crystallization, wherein R represents a monovalent metal or monovalent radical, cemented between two convergent elements made of glasses whose Abb V numbers lie between 45 and 62, the algebraic sum of the curvatures of the two cemented surfaces lying between 2 and 4 times the reciprocal of the focal length of the whole triplet component one cemented surface having a radius of curvature more than twice that of the other cemented surface.

8. An optical objective as claimed in claim 1, in which the crystalline alum incorporates aluminium sulphate combined with an alkaline sulphate.

9. An optical objective as claimed in claim 2, in which the crystalline alum incorporates aluminium sulphate combined with an alkaline sulphate.

10. An optical objective as claimed in claim 6, in which the crystalline alum incorporates aluminium sulphate combined with an alkaline sulphate.

11. An optical objective as claimed in claim 7, in which the crystalline alum incorporates aluminium sulphate combined with an alkaline sulphate.

12. An optical objective as claimed in claim 1, in which the crystalline alum consists of potash alum.

13. A triplet lens component as claimed in claim 3, in which the crystalline alum consists of potash alum.

14. A triplet lens component as claimed in claim 4, in which the crystalline alum consists of potash alum.

15. An optical objective as claimed in claim 6, in which the crystalline alum consists of potash alum.

16. An optical objective as claimed in claim 7, in which the crystalline alum consists of potash 17. An optical objective as claimed in claim 1, in which the crystalline alum consists of sodium alum.

18. A triplet lens component as claimed in claim 3, in which the crystalline alum consists of sodium alum.

19. A triplet lens component as claimed in claim 4, in which the crystalline alum consists of sodium alum.

20. An optical objective as claimed in claim 5,

7. in which the crystalline alum consists of sodium alum.

21. An optical objective as claimed in claim 6, in which the crystalline alum consists of sodium alum.

22. An optical objective having numerical data substantially as set forth in the following table:

Equivalent focal length 1.000 Relative Aperture F/2.7

Thickness or Relative Refractive Abb V Radius Air Separa- Partial tion Index 1in number Dispersion Di 0556 l. 613 59. 3 999 liz-3. 086

Dz .0185 l. 456 58.1 928 Ra+. 2629 D: 0648 1. 613 59. 3 999 Ri-H. 795

Si .0741 Ris-.8122

D4 .0231 l. 652 33. 5 1.060 Re+. 3485 Si .1000 R14-1.078

D5 0556 1. 613 59. 3 999 Rs-. 5324 In which R1, R2 represent the radii of curvature of the individual lens surfaces counting from the front (that is the side of the longer conjugate), the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, Di, D2 represent the axial thicknesses of the individual lens elements, and Si, S2 represent the axial lengths of the airgaps between the components.

23. An optical objective having numerical data substantially as set forth in the following table:

Equivalent focal length 1.000 Relative Aperture F/2.7

Thickness or Relative Refractive Abb V Radius Air Sepiira- Partial tion Index un number Dispersion Di .0812 1.644 48.3 1.025 R14-10. 148

Dz 0254 l. 097 30. 5 1. 007 124+. 4528 S2 0629 Rai-2. 169

D: 0964 1. 613 59. 3 999 Re. 2689 Ds 0507 l. 644 48. 3 1. 025 Rs. 8407 In which Ri, R2 represent the radii of curvature of the individual lens surfaces counting from the front (that is the side of the longer conjugate), the positive sign indicating that; the surface is convex to the front and the negative 8 sign that it is concave thereto, Di, D2 represent the axial thicknesses of theindividual lens elements, and Si, S2 represent the axial lengths of the airgaps between the components.

In which Ri, Rz represent the radii of curvature of the individual lens surfaces counting from the front (that is the side of the longer conjugate), the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, Di, D2 represent the axial thicknesses of the individual lens elements, and S1, Sz represent theaxial lengths of the airgaps between the components.

ARTHUR WARMISI-LAM. CHARLES GORRIE WYNNE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,588,612 Richter June 15, 1926 1,122,895 Florian Dec. 29, 1914 1,697,670 Wandersleb et al. Jan. 1, 1929 2,085,437 Michelssen June 29, 1937 1,541,407 Spannenberg June 9, 1925 535,897 Goerz et al. Mar. 19, 1895 1,025,766 Straubel May 7, 1912 1,713,708 Merte May 21, 1929 576,896 Rudolph Feb. 9, 1897 OTHER REFERENCES Partington, Textbook of Inorganic Chemistry, 1937 5th ed., pages 882-883.

Hackh, Hackhs Chemical Dictionary, 2nd ed., 1937, page 42, article on Alum Handbook of Chemistry and Physics, 1926, by Hodgman and Lange, page 723. 

